This invention relates to elastic fibers, fabrics and articles fabricated therefrom (e.g., disposable incontinence garments or diapers). The fibers and fabrics comprise at least one homogeneously branched substantially linear ethylene polymer having specific properties.
Fiber is typically classified according to its diameter. Monofilament fiber is generally defined as having an individual fiber diameter greater than about 15 denier, usually greater than about 30 denier per filament. Fine denier fiber generally refers to a fiber having a diameter less than about 15 denier per filament Microdenier fiber is generally defined as fiber having less than 100 microns diameter. The fiber can also be classified by the process by which it is made, such as monofilament, continuous wound fine filament, staple or short cut fiber, spun bond, and melt blown fiber.
A variety of fibers and fabrics have been made from thermoplastics, such as polypropylene, highly branched low density polyethylene (LDPE) made typically in a high pressure polymerization process, linear heterogeneously branched polyethylene (e.g., linear low density polyethylene made using Ziegler catalysis), blends of polypropylene and linear heterogeneously branched polyethylene, blends of linear heterogeneously branched polyethylene, and ethylene/vinyl alcohol copolymers.
Of the various polymers known to be extrudable into fiber, highly branched LDPE has not been successfully melt spun into fine denier fiber. Linear heterogeneously branched polyethylene has been made into monofilament, as described in U.S. Pat. No. 4,076,698 (Anderson et al.), the disclosure of which is incorporated herein by reference. Linear heterogeneously branched polyethylene has also been successfully made into fine denier fiber, as disclosed in U.S. Pat. No. 4,644,045 (Fowells), U.S. Pat. No. 4,830,907 (Sawyer et al.), U.S. Pat. No. 4,909,975 (Sawyer et al.) and in U.S. Pat. No. 4,578,414 (Sawyer et al.), the disclosures of which are incorporated herein by reference. Blends of such heterogeneously branched polyethylene have also been successfully made into fine denier fiber and fabrics, as disclosed in U.S. Pat. No. 4,2,922 (Krupp et al.), U.S. Pat. No. 4,990,204 (Krupp et al.) and U.S. Pat. No. 5,112,686 (Krupp et al.), the disclosures of which are all incorporated herein by reference. U.S. Pat. No. 5,068,141 (Kubo et al.) also discloses making nonwoven fabrics from continuous heat bonded filaments of certain heterogeneously branched LLDPE having specified heats of fusion.
However, fibers made from all of these types of saturated olefinic polymers are not xe2x80x9celasticxe2x80x9d, as that term is defined below, without incorporating additives or elastomers, thus limiting their use in elastic applications. One attempt to alleviate this problem by incorporating additives into the polymer prior to melt spinning is disclosed in U.S. Pat. No. 4,663,220 (Wisneski et al.), the disclosure of which is incorporated herein by reference. Wisneski et al. disclose fibrous elastomeric webs comprising at least about 10 percent of a block copolymer and a polyolefin. The resultant webs are said to have elastomeric properties.
U.S. Pat. No. 4,425,393 (Benedyk) discloses monofilament fiber made from polymeric material having an elastic modulus from 2,000 to 10,000 psi. The polymeric material includes plasticized polyvinyl chloride (PVC), low density polyethylene (LDPE), thermoplastic rubber, ethylene-ethyl acrylate, ethylene-butylene copolymer, polybutylene and copolymers thereof, ethylene-propylene copolymers, chlorinated polypropylene, chlorinated polybutylene or mixtures of those.
Elastic fiber and web prepared from a blend of at least one elastomer (i.e., copolymers of an isoolefin and a conjugated polyolefin (e.g., copolymers of isobutylene and isoprene)) and at least one thermoplastic is disclosed in U.S. Pat. No. 4,874,447 (Hazelton et al.), the disclosure of which is incorporated herein by reference.
U.S. Pat. No. 4,657,802 (Morman), the disclosure of which is incorporated herein by reference, discloses composite nonwoven elastic webs and a process for their manufacture. The elastic materials useful for forming the fibrous nonwoven elastic web include polyester elastomneric materials, polyurethane elastomeric materials, and polyamide elastomeric materials.
U.S. Pat. No. 4,833,012 (Makimura et al.), the disclosure of which is incorporated herein by reference, discloses nonwoven entanglement fabrics made from a three dimensional entanglement of elastic fibers, nonshrinkable nonelastic fibers, and shrinkable elastic fibers. The elastic fibers are made from polymer diols, polyurethanes, polyester elastomers, polyamide elastomers and synthetic rubbers.
Composite elastomeric polyether block amide nonwoven webs are disclosed in U.S. Pat. No. 4,820,572 (Killian et al.),, the disclosure of which is incorporated herein by reference. The webs are made using a melt blown process and the elastic fibers are made from a polyether block amide copolymer.
Another elastomeric fibrous web is disclosed in U.S. Pat. No. 4,803,117 (Daponte). Daponte discloses that the webs are made from elastomeric fibers or microfibers made from copolymers of ethylene and at least one vinyl monomer selected from the group including vinyl ester monomers, unsaturated aliphatic monocarboxylic acids and alkyl esters of these monocarboxylic acids. The amount of the vinyl monomer is said to be xe2x80x9csufficientxe2x80x9d to impart elasticity to the melt-blown fibers. Blends of the ethylene/vinyl copolymers with other polymers (e.g., polypropylene or linear low density polyethylene) are also said to form the fibrous webs.
Fabricated articles, such as incontinence garments, also benefit from use of elastic components. For example, U.S. Pat. No. 4,940,464 (Van Gompel et at.), U.S. Pat. No. 4,938,757 (Van Gompel et al.), and U.S. Pat. No. 4,938,753 (Van Gompel et al.), the disclosures of which are incorporated herein by reference, discloses disposable garments containing elastic gathering means and stretchable side panels. The gathering means and stretchable side panels are made from melt blown or film of block or graft copolymers (e.g., butadiene, isoprene, styrene, ethylene-methyl acrylate, ethylene-vinyl acetate, ethylene-ethyl acrylate or blends thereof.
While previous efforts to make elastic fibers and fabrics from olefinic polymers have focused on polymer additives, these solutions have potential detriments, including the increased cost of the additives, and incompatibility, resulting in substandard spinning performance.
We have discovered new elastic fiber and fabrics which do not need additives to be elastic. These new fiber and fabrics can be produced on conventional synthetic fiber or fabric processes (e.g., continuous wound filament, spun bond, and melt blown) and they can be used to produce highly elastic structures that can have recycle compatibility between elastic and non-elastic components. These fibers and fabrics are made from novel elastic homogeneously branched substantially linear ethylene polymers. These homogeneously branched substantially linear ethylene polymers have a processability in fiber and fabric processes similar to heterogeneously branched linear low density polyethylene, which means that the new elastic fiber and fabrics can be produced on conventional equipment.
The new elastic fiber has a permanent set of about 50% or less, or, stated another way, a percent recovery of at least about 50%. This property is surprisingly different than the response of fibers made from heterogeneously branched linear low density polyethylene where the percent permanent set seems to be generally greater than 50% and substantially independent of density, as illustrated in FIG. 2. The new elastic fiber is made from at least one homogeneously branched substantially linear ethylene polymer having:
a) a melt flow ratio, I10/I2,xe2x89xa75.63,
b) a molecular weight distribution, Mw/Mn, defined by the equation:
Mw/Mnxe2x89xa6(I10/I2)xe2x88x924.63,
c) a critical shear rate at onset of surface melt fracture of at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a linear ethylene polymer having about the same I2 and Mw/Mn, and
d) a density less than about 0.90 g/cm3.